Originally Posted by daveryanwyoming .
I agree with the overall gist of your post but in addition to Tony's comments, the points above are pretty misleading.
Blowing up is a short term fatigue of key systems things and can happen just as easily by trying to overpace a 40K TT and blowing up before the finish or a five minute bridging effort as it can in a short intense L6/AWC burst. IOW, you can just as easily blow up during primarily slow twitch sections or primarily fast twitch sections and it has a lot more to do with specific fitness for the type of effort and pacing than the muscle fiber type.
And as you acknowledged above, Bonking is a fuels management, primarily glycogen and blood glucose fuels management issue, I guess you could say it's a slow twitch thing from the standpoint that it's a longer term issue and you can't really bonk in a minute of hard effort unless you were already seriously glycogen depleted, but again tying it to muscle fiber makeup misses the point.
FWIW, in some sports nutrition circles they further differentiate bonking and hitting the wall. The former being an acute shortage of blood glucose to the brain with the resulting mood shifts, irritability, tunnel vision, sense of doom, etc. The latter being depletion of muscle glycogen and inability to fuel muscle contractions primarily via sugars. They're often but not always connected to one another. IOW, it's possible to bonk with legs that still have plenty of glycogen on board but you're not currently fueling your brain and it's possible to have enough blood glucose and liver glycogen to feed the brain adequately but the legs are depleted. That can happen during periods of frequent hard and long training and racing when the rider isn't keeping up with glycogen resynthesis, blood sugar can be all right since you can get blood sugar up very quickly by eating on the bike but muscle glycogen stores can be depleted from previous work and glycogen synthesis is a slower process. Anyway, interesting take on things and not how I previously thought about bonking on the bike.
-Dave